We're still working on this, new images from the last few days are being served at wepb at 90% quality to make sure the quality is there. The problem with this is that the increase in bandwidth and cache this causes is around 10x what it costs at 75% quality. This also means that loading times are 10x longer!
We've had an idea to try and use AVIF instead of webp, so we're just testing that out, and it's looking pretty promising for static images.
We're looking at something like 75% quality on AVIF which is as good as, or better then, 90% quality at webp whilst also being smaller in file size.
There's still some more testing to do, and we won't make any sweeping changes before the weekend.